The present invention relates in general to the treatment of fusible materials, such as a solder preform, and in particular, to a new and useful process for shaping the surface of solid fusible material to facilitate the attachment of a member requiring precise alignment to a substrate.
Traditionally, soldering is a process in which a joint is made between two or more metal parts. The metal solder which is used to form a solder joint, must, in its liquid state, form inter-metallic phases with the material of the metal parts. In some cases, it proves advantageous to place solid solder material on a surface, or substrate, and lay the parts to be joined onto the solder, and subsequently join them. This serves to join the two members as well as to fix the joint to the substrate. The greatest issue in any joining process is the positioning of the parts before and after they are joined. To ensure proper positioning of the parts, a groove or track in the surface of the solid solder would be used to prevent the part from changing orientation during the fusing process. The forming of this track is now the most important part of the entire soldering process and the groove ensures a particular spatial orientation of the part, for example, the distance between the part and the substrate. In applications such as optical fiber attachments, this distance is critical to the performance of the end product.
There are a few methods of shaping the surface of the solder. They are based on a forming shape being pressed against and removed from the solder surface, leaving the desired shape for the particular application. U.S. Pat. Nos. 3,750,265 and 4,752,027 both use rollers as a method of forming the shape in the surface of solder. The former uses rollers with protrusions along the circumferences to create depressions in a strip of solder wire, while the latter uses rollers to flatten the surfaces of solder bumps on a printed circuit board. U.S. Pat. No. 4,997,122 uses a heated tool to pierce the surface of the solder to fuse it and subsequently withdraw the tool, leaving a permanent shape in the solder.
This invention solves the issue of creating a track in a solid solder material to aid in reducing physical interferences during the process of accurate positioning of a part for use in a fiber optic alignment and attachment application. The solder material, a preform, is laid onto a substrate material. The preform is subjected to heat energy sufficient to cause fusing, forming a solder globule.
A tool, with a treatment surface with a desired shape and at a temperature below that of the fusing point of the preform, is maneuvered such that the treatment surface penetrates the fused preform. The preform is allowed to cool and solidify and the treatment surface withdrawn from the surface of the preform, leaving an impression with the desired shape in the preform surface. The entire process occurs in a chemically reducing atmosphere, known as a cover gas, to prevent the formation of oxide layers during the fusing process. The cover gas is preferred to liquid flux since, in this application, there can be no residue from the solder process. The heat energy may be in the form of radiated infrared energy, resistive energy, or heat transfer from a hot gas.
For most applications it is not easy to control the shape of the formed solder, so an object of the present invention is a mold that is used to contain the solder to a region defined by the extends of the mold, which are typically similar to the projected size of the solder pad upon which the solder is fused. The mold tool is applied to the solder region using an automatic actuator before the solder is liquefied. After the mold tool is in place the forming process commences as per the following described preferred embodiment of the invention.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.